Depression is a debilitating and life-threatening disease that affects millions of people worldwide. The clinically available antidepressants share the same core mechanisms of enhancing monoamine transmission in the brain. The high prevalence of the disease and limited effectiveness of current treatments indicate the importance and urgency to find novel therapeutic targets for the treatment of depression. Clinical and laboratory observations over the last decade indicate that the endocannabinoid (eCB) system represents a promising target for the pharmacotherapy of depression. The CB1 cannabinoid receptor antagonist rimonabant increases the incidence of anxiety and depression in clinical trials for the treatment of obesity, whereas cannabis improves mood in humans and CB1 agonists produce antidepressant-like effects in animal models of depression. Inhibitors of eCB inactivation amplify endogenous eCB activity in a temporal- and spatial-specific manner and should be superior to direct CB1 receptor agonists as therapeutic agents. The eCB ligand 2- arachidonoylglycerol (2-AG) is inactivated by monoacylglycerol lipase (MAGL) and serine hydrolase alpha- beta-hydrolase domain 6 and 12 (ABHD6/12). However, it remains unknown whether inhibition of MAGL or ABHD6/12 produces antidepressant effects in animal models of depression. Addressing this important question became possible now with the recent synthesis of selective and potent MAGL inhibitor JZL184 and ABHD6 inhibitor WWL123. Using chronic mild unpredictable stress (CUS) as an animal model for depression, we test the hypothesis that the 2-AG signaling is impaired in depression and the blockade of 2-AG inactivation with MAGL or ABHD6 inhibitors produces antidepressant-like effects by rescuing the deficiency in 2-AG signaling. We will test this hypothesis through two specific aims: (1) Test the hypothesis that 2-AG signaling is impaired in CUS model of depression; and (2) Test the hypothesis that MAGL or ABHD6 blockade produces antidepressant-like effects by rescuing CUS-induced impairment of 2-AG signaling. Under the first Aim, we will record 2-AG-mediated electrophysiological responses to interrogate ongoing status of 2-AG signaling in the hippocampus in a CUS model of depression. Under the second aim, we will examine whether in vivo chronic or subchronic administration of JZL184 or WWL123 produces antidepressant-like effects by rescuing CUS- induced deficiency in eCB signaling. We will also examine whether MAGL knockout mice exhibit antidepressant-like phenotypes. Completion of this investigation will lead to the identification and validation of new therapeutic targets for pharmacotherapy of depression and will provide an improved understanding of the mechanisms of mood regulation and the etiology of depression. PUBLIC HEALTH RELEVANCE: The proposed research investigates the antidepressant effects of inhibitors of endocannabinoid inactivation in an animal model of depression. Completion of this project will contribute knowledge at both mechanistic and practical levels for the development and testing of therapeutic strategies for pharmacological intervention of depression.